devicePixelRatio className tweak

htmlDprTweak.js

/**
 * `html` class tweaking
 * if `devicePixelRatio` was 2, switch html's class
 * from `dpr-1` to `dpr-2`
 */
(function() {

  var html = document.getElementsByTagName("html")[0];

  /* helpers */

  var hasClass = function(node, cls) {
    return new RegExp("(\\s|^)" + cls + "(\\s|$)").test(node.className);
  };

  var addClass = function(node, cls) {
    if (hasClass(node, cls)) {
      return;
    }
    return node.className = "" + node.className + " " + cls;
  };

  var removeClass = function(node, cls) {
    if (!hasClass(node, cls)) {
      return;
    }
    node.className = node.className
      .replace(new RegExp("(\\s|^)" + cls + "(\\s|$)"), " ")
      .replace(/\s+/g, " ").replace(/^\s|\s$/, "");
  };

  /* tweak `html` className */

  (function() {
    var dpr = window.devicePixelRatio;
    if (!dpr) {
      return;
    }
    if (dpr >= 1.5) {
      removeClass(html, 'dpr-1');
      addClass(html, 'dpr-2');
    }
  }());

}());